In baby diapers and other similar products, elastic components are used to adapt the article to the body shape of the user.
For this purpose polymer films with elastic properties are used, i.e. polymer films that can be stretched and deformed by elongation remaining in the substantially elastic range, so that when the film is released it returns approximately to its original configuration, or has a limited permanent deformation, typically within 10% of the initial length after 3 elongation cycles at 80%.
From a film of this type elastic strips are produced which are applied to the diaper to give it the necessary fit and to allow it to be adapted or applied to the user. In baby diapers elastic films of this type are used to produce the closing tabs of the diaper. In “training pants” used today to facilitate the passage from using a diaper to using normal pants, strips of elastic film are used to form the side bands of the article, which is worn like normal pants, but has the structural and functional properties of a diaper. In particular, in this application the article has large surfaces made of elastic polymer film.
As contact of the polymer film with the skin would be unpleasant and, especially in use in baby diapers, might give rise to phenomena of cutaneous irritation, systems have been studied to coat the polymer film with textile fibers. The coating in textile fibers also has the function of giving the product a better “handle”, not only for the person wearing it, but also for the person who handles it. Fiber coatings are therefore used also on elastic films used for components of the diaper that do not come into contact with the skin of the user.
U.S. Pat. No. 5,422,172 discloses a laminate formed of an elastic film bonded to a layer of nonwoven and a relative method of production. The polymer film is extruded directly in the nip of a calender, through which one or two card webs are fed. The fibers are bonded directly to the extruded film. This process requires complex machinery, as the film must be extruded directly at the mouth of the calender. Moreover, when the product thus obtained is pulled and elongated this causes breakage of the fibers.
According to other techniques the web of fibers is bonded to a preformed film. This type of product has not proved to be satisfactory, as if the nonwoven is applied to the polymer film holding the latter in the stretched position, when the laminate obtained is released and the film returns to its non-elongated position, the nonwoven becomes wrinkled. Moreover, in these techniques the film is elongated, i.e. pre-stretched in machine direction (MD), i.e. in the direction parallel to the direction of feed of the material. On the other hand, when the semi-finished product is used to produce absorbent articles or garments (such as diapers or the like), elasticity in a cross direction (CD), or prevalently cross direction, is generally required. This is because in the conformation phase of the diaper, if the elastic product is fed aligned with the diaper, the production speed is much greater than the speed which would be achieved if the elastic band were to be fed in the cross direction and then rotated.
If the film is laminated to the nonwoven web without first having been stretched and elongated, the nonwoven obstructs elongation of the film during use and the fibers can detach or break. Alternatively, elastic nonwovens would have to be used, but these have a high cost.
US-A-2003/0105446 describes a composite laminated product comprising an intermediate polymer film laminated to two webs of fibers. Also in this case the film is extruded directly in the machine that performs lamination with at least one of the two layers of fibers. The composite product is then subjected to elongation in the elastic range to break the fibers and give the finished article the elasticity of the film. The possibility of perforating the film is also described. This production process is complex and unsatisfactory due to breakage of the fibers, which on the other hand is necessary to obtain a semi-finished product with adequate elastic properties at the end of the production line.
Further methods for producing an elastic film and fiber laminate are described in US-A-2003/0084986 and in U.S. Pat. No. 6,537,930, US-A-2003/0022582 and in U.S. Pat. No. 6,255,236.
EP-B-0737462 describes a composite material composed of a non-elastic polymer film on which a layer of flocked fibers is formed. This material is used in particular as a topsheet in feminine sanitary napkins. The film has a perforation to allow the passage of body fluids.